UDP-glucose dehydrogenase (UGDH) is a unique, essential enzyme with the central role of providing UDP- glucuronate, a rate-limiting precursor for plasma membrane hyaluronan synthesis, Golgi proteoglycan production, and ER-localized modification of hormones for elimination. Our laboratory has shown that insufficiency of UGDH contributes to loss of control of intracellular steroid levels, and dysregulated tumor cell growth rate in prostate cancer. It is not known how the cytosolic UDP-glucuronate is partitioned to its respective fates in the high levels needed for specifically timed product formation, nor how UGDH activity is controlled to limit competition with other pathways. Our hypothesis for this proposal is that hexameric and dimeric units of UGDH sense metabolic status of the cell and respond with increased or decreased enzymatic activity. Information for molecular sensing is conveyed partly through differential protein-protein interactions that occur upon exposure of the dimer-dimer interface. We will test this with two aims. Aim 1: Determine the functional outcome of specific UGDH interactions with components of the androgen elimination pathway. We will directly measure interactions of UGDH with hyaluronan synthase, the Golgi UDP-xylose transporter, and the ER UDP-glucuronate transporter, as the three proteins that mediate the demands for UDP-glucuronate flux. We will quantify UDP-glucuronate, steroid-glucuronide, notch glycosylation and hyaluronan production, which will respectively report overall UGDH activity, and functional distribution to the ER for androgen elimination, the Golgi for proteoglyca secretion, or the plasma membrane for hyaluronan synthesis. Aim 2: Characterize and validate the UGDH interactome using an unbiased approach. We will use mass spectrometry to identify proteins that differentially co-fractionate by size exclusion chromatography with our well- characterized hexameric and dimeric point mutants. As a complementary approach, we will identify proteins that cross-link with hexameric versus dimeric UGDH point mutants that incorporate a photo-activatable crosslinker as a non-natural amino acid. Validated interactions and/or post-translational modifications will be used to design strategies for selective partitionin of UDP-glucuronate to favor hormone elimination in future preclinical studies of prostate cancer.